1. Field of the Invention
The present invention relates to an illumination device, and more particularly to an illumination device using an optical fiber.
2. Description of the Related Art
An illumination device using an optical fiber has been recently widely used for interior/exterior designs. The optical fiber illumination device may be used in locations with high humidity or high temperature, because an optical fiber generates no heat, has an excellent moisture-proof/heat-resistant characteristic, and allows the light input from a light source to be transferred to a position far away from the light source. In the case where the light source and the to-be-illuminated area are spaced far apart from each other, the optical fiber illumination device has an advantage in that the light source, power supply for driving the light source, and a driving circuit can be disposed at a position not subjected to the influence of moisture or temperature.
Japanese Laid-Open Patent Publication No. 2001-35201, to Tamaoki Satoshi, published on Feb. 9, 2001, entitled “Illumination Device”, discloses an illumination device using a light emitting diode and an optical fiber array, in which the light emitting diode has a light emitting surface directly facing one end (a light receiving end) of the optical fiber array, and the light coupled within the optical fiber array is emitted from the other end (a light emitting end) of the optical fiber array.
However, in Satoshi, much of the light output from the light emitting diode is lost without being coupled with the optical fiber array.
Especially in the case where the area of a light receiving end of an optical fiber or an optical fiber array is very small compared to the light divergence angle of a light source, or the area of the light emitting surface of the light source is very large compared to the area of the light receiving end of the optical fiber or the optical fiber array, such optical coupling loss significantly increases.
FIG. 1 is a view illustrating optical coupling loss between a light emitting diode and an optical fiber in a conventional apparatus. A light emitting surface 112 of a light emitting diode 110 and an end 122 of an optical fiber 120 face each other, and the light divergence angle of the light emitting diode 110 is very large compared to the area of the end 122 of the optical fiber 120. Thus, only some of the light output from the light emitting diode 110 is coupled within the optical fiber 120, and much of the output light is lost without being coupled with and transmitted by the optical fiber 120.
FIG. 2 is a view illustrating optical coupling loss between multiple light emitting diodes and an optical fiber. Light emitting surfaces of red, green, and blue light emitting diodes 132, 134, and 136 face one end 142 of an optical fiber 140, and the light divergence angle of each of the light emitting diodes 132, 134, and 136 is very large compared to the area of the end 142 of the optical fiber 140. Thus, only some of the light output from each of the light emitting diodes 132, 134, and 136 is coupled within the optical fiber 140, and much of the output light is lost without being coupled with the optical fiber 140. Also, when the optical fiber 140 is positioned nearer to the red light emitting diode 132 than to the green and blue diodes 134 and 136, as shown FIG. 2, i.e. when the longitudinal axis of the optical fiber 140 is aligned toward the red light emitting diode 132, such alignment causes color non-uniformity (the prominence of red) in the light output from the optical fiber 140.